Field of the Invention
The invention relates to the field of electrotechnology and can be used in rotary electric machines, particularly electric motors and generators.
Description of the Background Art
In more recent times rotary electric machines, particularly electric motors, but generators as well, are often designed as so-called brushless machines, whereby accordingly direct electric contacting of a rotor by brushes is not necessary. The rotor can be equipped with permanent magnets, which are driven in a rotating magnetic field of the stator. The stator has stator windings for this purpose, which are controlled accordingly to generate a rotating magnetic field. Control methods are often used in this case, for example, via pulse width modulation (PWM), whereby the stator winding can be realized typically by semiconductor circuits with metal-oxide-semiconductor field-effect transistors (MOSFETs), IGBTs, or thyristors. Largely freely selectable field configurations and accordingly also dynamically rotating fields can be created via pulse width modulation.
Because electrical step signals that are to simulate, for example, a sinusoidal control characteristic as accurately as possible are produced particularly during the use of pulse width modulation in the kHz to MHz range, the emission of electromagnetic waves in the area of the windings and lines must be expected.
This electromagnetic effect can act on the control circuit, for example, but also on other units and consumers in the vicinity of the rotary electric machine, which is generally undesirable. For this reason, emphasis continues to be placed on the demand for increased electromagnetic compatibility or as low a transmitting activity as possible. Accordingly, interference in electric machines should be largely eliminated.